In the deep processing of dyeing and finishing of cotton and other cellulose fibers, the quality of the pre-treatment is greatly related to the quality of the dyeing and finishing results. If the pretreatment is not good, it will affect the basic whiteness, penetration and absorption index, dyeing leveling performance, etc. of the semi-finished products at the least; it will greatly reduce the strength of the fiber, causing the semi-finished products to be obviously brittle, and even serious. Breaking fibers (or creating holes in fabric). Once such fiber brittleness occurs, it will not only be difficult to repair, but may also cause the textile to be scrapped.
Due to on-site supervision of pre-processing quality, on the production line, it is not as easy to judge intuitively and quickly as dyeing and post-finishing, and the quality semi-inspection work can usually only be carried out. It is a certain proportion of random inspections. Moreover, some quality problems caused by poor pre-treatment will be intertwined with the quality of dyeing, making the cause analysis particularly complicated. Some of these defects are very difficult to repair and the cost of repair is high, not to mention the more serious consequences caused by irreparability after the fiber is damaged and destroyed.
01 Sudden quality problems under mature technology
In the initial trial dyeing of new textile products (or new varieties) If the process and formula design are not yet mature and reasonable enough, including the chemical raw materials selected, if they do not meet the new requirements for new products, it should be understandable and explainable if there are deficiencies in quality requirements during trial production. . At this time, it is easier to be clear and understand the direction and ideas for further improvement.
Once it enters regular large-scale production and has proven to be a mature and stable process and formula through mass production, there will usually not be any major problems. Therefore, in order to ensure the high stability of large-scale production, the production technology departments of dyeing and finishing companies are very cautious about the pre-processing process, and generally will not casually change the processes and formulas that have been confirmed to be mature and stable, and Including varieties of chemical raw materials and their supply companies.
However, sometimes you will be disturbed by sudden blemishes that are somewhat inexplicable, and there may also be the taboo problem of fiber brittleness (or even holes). Since it has been identified as a non-process formula design factor, when such a situation occurs, the first suspicion is that it is related to the chemical raw materials. In particular, attention is paid to whether there are any quality problems with the relevant additives, so it is easy to cause disputes.
However, if chemical raw materials such as additives are rechecked, there may not be any problems. For testing chemical raw materials such as auxiliaries, dyeing, finishing and auxiliary companies that have begun to take shape can now achieve rapid response and clear detection. It is also necessary to mention that in the current market climate of additives, where supply exceeds demand and customers sell on credit first and pay later, almost every chemical additive company does not know how to, and does not dare to They treat the credibility and reputation of corporate survival as child’s play.
At this time, it is easy to get confused even in the direction of finding the cause of this sudden fiber brittleness phenomenon that seems to be “out of common sense”. Because nowadays, in the planned operation and management of large-scale production of dyeing and finishing enterprises, especially when it comes to the business type of dyeing and finishing processing, it is almost required to solve the problem quickly; although the probability of occurrence of sudden brittle fiber defects is not High, but once it occurs, it is often an event that makes specific managers panic and fear the most, because it contains large economic losses and liability issues.
02 Influencing factors of sudden fiber brittleness
Fiber brittleness occurs for no reason, of course It has no scientific basis and is not objective. There is no doubt that there must be factors of inevitability hidden behind it, but they may be ignored or even ignored. In addition, it is also necessary to remind that it is not ruled out that there are cases that violate the common sense scope requirements and are in the “gutter”. “The boat capsized”.
1. The problem of water quality fluctuations is easy to be ignored, but it has a greater impact and is likely to suddenly appear among the factors affecting the fluctuations. The first is the iron ion content of the production water. As we all know, calcium, magnesium, iron and other metal ions in water have a close impact on all aspects of dyeing and finishing production; among them, the number one factor that can cause embrittlement damage to cellulose fibers during pre-treatment is iron ions.
Hydrogen peroxide is an indispensable basic chemical raw material in today’s pretreatment. Hydrogen peroxide decomposes slowly at room temperature, but under conditions of heat and light, or after adding alkali, H2O2 is activated and decomposes rapidly, as follows As shown in the formula:
The above reaction promotes the formation of free radicals, which in turn intensifies the decomposition reaction.
It can be seen from the formula that when the amount of caustic soda is increased, HOO will increase, which will improve the bleaching effect. However, with the increase in alkali concentration and the presence of metal ions, the decomposition rate of H2O2 will accelerate rapidly. Without control, Not only is the hydrogen peroxide wasted, but the whiteness of the fabric is reduced, and the cotton fibers are even brittle.
The content of calcium, magnesium, and iron metal ions in water is in principle determined by the water source of the water supply. Therefore, the quality of production water is usually very difficult to detect and sample.Low, if the operation can be strictly controlled, safety can still be guaranteed. First of all, the diluted solution with the ratio specified by the first-level enterprise standard must be prepared in advance, and the distribution must be strictly implemented; secondly, when used in the workshop, the dilute solution should be further diluted according to the ratio specified by the second-level workshop standard, stir evenly, and then add to the machine. When adding materials into the machine, it is forbidden to have direct contact between the dilute acid solution and the cloth surface; thirdly, carefully conduct online testing of the PH value of the cloth surface.
It should be highly noted that during the actual on-site operations on the front line of the production workshop, some car blocking operators (especially some new employees who lack experience and lessons) may also occur. Because nothing major happened for a long time, I became careless and relaxed, and no longer strictly implemented the operating procedures, especially when entering and leaving the workshop management, late-night shifts when there were fewer technicians, etc.
3.2 Insufficient washing strength after oxygen bleaching and its impact. The pre-treatment of certain types of gray fabrics and printed products will be included in the process after oxygen bleaching. A drying step. It is very simple and clear that whether there is sufficient water washing (including hot water washing and cold water washing) after oxygen bleaching is extremely important and direct for the complete removal of alkali, hydrogen peroxide and other chemical residues during oxygen bleaching on gray fabrics. The more thoroughly it is removed, the better it can ensure the quality requirements for future dyeing or printing, as well as finishing. Although the neutralization treatment can counteract the alkali agent on the gray fabric and reduce the PH value on the fabric, it will be converted into salt and may not be reliable in removing residual hydrogen peroxide and other additives. Therefore, water washing cannot replace water washing but can only be used as a supplement to water washing because it can reduce the number of water washings and thus play a certain role in saving water.
Because water washing is a process that is easy to omit in process execution but difficult to detect, and it is difficult to conduct effective review afterwards, it is also one of the key contents in on-site management. If the washing intensity is insufficient or even reduced, during the drying process, the residual alkali and hydrogen peroxide on the gray cloth will become more concentrated on the cloth due to the rapid evaporation of water. Increase, once it is higher than the critical point, the decomposition of the remaining hydrogen peroxide will become uncontrolled under the high temperature environment of the dryer. From the chemical reaction formula between the above alkali agent and hydrogen peroxide, it can be known that this will inevitably lead to the decomposition of cellulose fibers. The problem of brittle damage occurs in this link.
03 The Importance and Necessity of Job Training
Enterprises always hope to recruit skilled employees, but in the current reality, But it may not be able to meet the company’s employment requirements. And even for some so-called “skilled” employees, it may be a relative term. Differences in dyeing and finishing methods caused by differences in textile types. Although the basic principles of dyeing and finishing are the same, the specific processes, formulas, production processes, vehicle blocking operations, etc. are quite different. For example, a skilled worker for long lathe pad dyeing may not be skilled in dip dyeing or jig dyeing methods and operating procedures, and vice versa. Of course, not to mention unskilled workers who have only worked in other industries and are not in this major.
The current turnover of employees in various enterprises is both frequent and common, and the objective reality of the recruitment and employment market means that dyeing and finishing companies often have to accept even unskilled employees. Therefore, whether on-the-job training and on-site management are necessary Once in place, the impact is both significant and direct.
In view of the analysis of the above influencing factors, the requirements include: Workers on the front line of production should all have specific knowledge of the physical and chemical properties of each chemical raw material used. Especially for the additives of a new product, or the additives newly used by our factory, its properties, performance, functions, characteristics, safety requirements and other aspects, as well as the resulting newly formulated production processes and operating procedures wait. The enterprise’s production technology department should provide corresponding on-the-job training for employees, clearly standardize operating regulations and strengthen on-site management, and guide the progress of large-scale production with the concept of “prevention is better than cure”. </p